Method for manufacturing fluoropolymers

ABSTRACT

The invention pertains to a method for making a fluoropolymer comprising an aqueous emulsion polymerization of one or more fluorinated monomers wherein said aqueous emulsion polymerization is carried out in the presence of at least one cyclic fluorocompound of the following formula (I): 
     
       
         
         
             
             
         
       
     
     wherein X 1 , X 2 , X 3 , equal or different from each other are independently selected among H, F, and C 1-6  (per)fluoroalkyl groups, optionally comprising one or more catenary or non-catenary oxygen atoms; L represents a bond or a divalent group; R F  is a divalent fluorinated C 1-3  bridging group; Y is a hydrophilic function selected among anionic functionalities, cationic functionalities and non-ionic functionalities.

CROSS-REFERENCE TO RELATED CASES

The present patent application is a U.S. national stage applicationunder 35 U.S.C. §371 of International Application No. PCT/EP2009/058530,filed Jul. 6, 2009, which claims priority benefit of European patentapplication no. 08159936.7, filed on Jul. 8, 2008, and of Europeanpatent application no. 08168221.3, filed on Nov. 3, 2008, the wholecontent of each of these applications being incorporated herein byreference for all purposes.

TECHNICAL FIELD

The present invention pertains to a method of making fluoropolymerdispersions, to fluoropolymer dispersions therefrom and to cyclicfluorosurfactants useful in said method.

BACKGROUND ART

Fluoropolymers, i.e. polymers having a fluorinated backbone, have beenlong known and have been used in a variety of applications because ofseveral desirable properties such as heat resistance, chemicalresistance, weatherability, UV-stability etc.

A frequently used method for producing fluoropolymers involves aqueousemulsion polymerization of one or more fluorinated monomers generallyinvolving the use of fluorinated surfactants. Frequently usedfluorinated surfactants include perfluorooctanoic acids and saltsthereof, in particular ammonium perfluorooctanoic acid.

Recently, perfluoroalkanoic acids having 8 or more carbon atoms haveraised environmental, concerns. For instance, perfluoroalkanoic acidshave been found to show bioaccumulation. Accordingly, efforts are nowdevoted to phasing out from such compounds and methods have beendeveloped to manufacture fluoropolymer products using alternativesurfactants having a more favourable toxicological profile.

Several approaches have been recently pursued to this aim, typicallyinvolving fluorosurfactants comprising a perfluoroalkyl chaininterrupted by one or more catenary oxygen atoms, said chain having anionic carboxylate group at one of its ends.

Examples of these compounds which are endowed with improvedbioaccumulation profile over perfluoro alkanoic acids having 8 or morecarbon atoms can be found notably in US 2007276103 (3M INNOVATIVEPROPERTIES CO) 29 Nov. 2007, US 2007015864 (3M INNOVATIVE PROPERTIES CO)18 Jan. 2007, US 2007015865 (3M INNOVATIVE PROPERTIES CO) 18 Jan. 2007,US 2007015866 (3M INNOVATIVE PROPERTIES CO) 18 Jan. 2007.

It would thus be desirable to find alternative fluorinated surfactantsthat can be used in the emulsion polymerization of fluorinated monomerswhich desirably show lower bioaccumulation/biopersistence than perfluoroalkanoic acids having 8 or more carbon atoms.

It would further be desirable that the surfactant properties of saidalternative fluorinated surfactants be such that polymerization can becarried out in a convenient and cost effective way, using equipmentcommonly used in the aqueous emulsion polymerization of fluorinatedmonomers with traditional surfactants.

SUMMARY OF THE INVENTION

It has been found that cyclic fluorocompounds of the following formula(I):

as detailed below, are effective in the aqueous emulsion polymerization,even when used without the addition of other surfactants such asperfluoroalkanoic acids and salts thereof.

Moreover, the Applicant has surprisingly found that above mentionedcyclic fluorocompounds (I) have significantly improved biopersistencebehaviour over perfluoroalkanoic acids derivatives, so that theirtoxicological profile is much improved.

Finally, these cyclic fluorocompounds (I) have a higher volatility overperfluoroalkanoic acids derivatives, so that their residues in finalparts obtained from fluoropolymer dispersions containing the same can besignificantly reduced.

Thus, in one aspect, the invention relates to a method for making afluoropolymer comprising an aqueous emulsion polymerization of one ormore fluorinated monomers wherein said aqueous emulsion polymerizationis carried out in the presence of at least one cyclic fluorocompound ofthe following formula (I):

wherein X₁, X₂, X₃, equal to or different from each other areindependently selected among H, F, and C₁₋₆ (per)fluoroalkyl groups,optionally comprising one or more catenary or non-catenary oxygen atoms;L represents a bond or a divalent group; R_(F) is a divalent fluorinatedC₁₋₃ bridging group; Y is a hydrophilic function selected among anionicfunctionalities, cationic functionalities and non-ionic functionalities.

The hydrophilic function Y can be notably selected among non-ionicfunctions of formulae —(OR_(H))_(n)—OH, wherein R_(H) is a divalenthydrocarbon group, and n is an integer of 1 to 15.

As an alternative, the hydrophilic function Y can be notably selectedamong cationic functions of formulae:

wherein R_(n), equal or different at each occurrence, represents ahydrogen atom or a C₁₋₆ hydrocarbon group (preferably an alkyl group), Eis a C₁₋₃ divalent hydrocarbon group and X_(b)— is an anion selectedamong OH⁻, Cl⁻, Br⁻, I⁻.

Nevertheless, the hydrophilic function Y is preferably selected amonganionic functions, in particular among those of formulae:

wherein X_(a) is H, a monovalent metal (preferably an alkaline metal) oran ammonium group of formula —N(R′_(n))₄, wherein R′_(n), equal ordifferent at each occurrence, represents a hydrogen atom or a C₁₋₆hydrocarbon group (preferably an alkyl group).

Most preferably, hydrophilic function Y is a carboxylate of formula(3″), as above detailed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of theinvention, reference will now be made to the accompanying drawings inwhich:

FIG. 1 depicts the ¹⁹F-NMR spectrum recorded on a compound (B);

FIG. 2 depicts the ¹⁹F-NMR spectrum of compound (E);

FIG. 3 depicts the ¹⁹F-NMR spectrum recorded on compound (H);

FIG. 4 illustrates a sketch of the surface tension (in mN/m) as afunction of concentration (in g/l) for compounds Va (with X_(a)═NH₄),VIIa (with X_(a)═NH₄) and ammonium perfluorooctanoate (APFO);

FIG. 5 illustrates plasma concentrations for compound VIIa (X_(a)═NH₄),Va (X_(a)═NH₄), XIII (X_(a)═NH₄) and APFO as a function of time;

FIG. 6 depicts the thermogravimetric analysis (TGA) traces as % weightloss as a function of temperature (in ° C.) for APFO (1), compound Va(X_(a)═NH₄) (2) and VIIa (X_(a)═NH₄) (3);

FIG. 7 depicts the ¹⁹F-NMR spectrum recorded on ammonium salt (compoundXIII, with X_(a)═NH₄);

FIG. 8 depicts the thermogravimetric analysis (TGA) traces as % weightloss as a function of temperature (in ° C.) for APFO (1) and compoundXIII (X_(a)═NH₄) (2); and

FIG. 9 provides TGA isothermal scans under vacuum carried out oncompound XIII (X_(a)═NH₄) at T=150° C. and 180° C.

DETAILED DESCRIPTION

According to a first embodiment of the invention, the cyclicfluorocompound complies with formula (II) here below:

wherein X₁, X₂, X₃, Y and R_(F) have the same meaning as above defined.

More preferably, the cyclic fluorocompound complies with formula (III)here below:

wherein R_(F), X₁, X₂, X₃, and X_(a) have the same meaning as abovedefined.

According to a first variant of this preferred embodiment, the cyclicfluorocompound complies with formula (IV):

wherein X′₁ and X′₂, equal to or different from each other, areindependently a fluorine atom, a —R′_(f) group or —OR′_(f) group,wherein R′_(f) is a C₁₋₃ perfluoroalkyl group, preferably with theprovision that at least one of X′₁ and X′₂ are different from fluorine,and R_(F) and X_(a) have the same meanings as above defined.

Compounds of formula (IV) can be notably obtained by reaction ofperfluoroallylfluorosulfate derivatives of formula:

with a bis-hypofluorite of formula:

so as to obtain corresponding adduct of formula.

which yields by hydrolysis the target compound (IV).

Hydrolysis of above mentioned adduct is preferably accomplished byalkaline hydrolysis with an aqueous inorganic base, e.g. with aqueousKOH, optionally followed by treatment with an aqueous acidic solution(e.g. HCl_(aq)) for obtaining carboxylic acids and/or furtherneutralisation for introducing required counter-cation onto thecarboxylic group.

In an alternative method for preparing cyclic fluorocompounds of formula(IV) here above, a cyclic fluoroolefin is reacted with carbonyl fluoridein the presence of fluorides, as sketched in scheme herein below:

wherein X′₁, X′₂, R_(F) have the meaning as above defined.

So obtained carbonyl fluoride derivative can be easily hydrolyzed toyield the target compound (IV).

In a further alternative method, cyclic fluorocompound of formula (IV)can be prepared by adding to a cyclic fluoroolefin methanol forobtaining a cyclic fluorinated methanol derivative, as sketched in thescheme herein below:

wherein X′₁, X′₂ and R_(F) have the meaning as above defined. Cyclicalcohol derivative can be further transformed in compound (IV) viafollowing steps:(i) esterification of the cyclic alcohol with a fluorinated acylfluoride yielding the corresponding ester:

(ii) complete fluorination of all C—H bonds in C—F bonds of this latterto yield corresponding perfluorinated ester compound:

(iii) decomposition of the perfluoroester to yield the correspondingperfluoroacyl compound:

(iv) hydrolysis and treatment with a base for yielding the correspondingcarboxylate derivative (IV):

wherein in all formulae herein above X′₁, X′₂, R_(F) and X_(a) have themeaning as above defined; R*_(F) is a (per)fluorocarbon group.

Any other process enabling complete fluorination of the C—H bonds, butpreserving alcohol/carboxylic functionality under protected form can bealso suitable for transforming above mentioned cyclic fluorinatedmethanol derivative in compound (IV).

The cyclic fluorocompound (IV) of the first variant of this preferredembodiment more preferably complies with formula (V):

wherein X′₁, X′₂, X′₃, X′₄, equal to or different from each other areindependently a fluorine atom, —R′_(f) or —OR′_(f), wherein R′_(f) is aC₁₋₃ perfluoroalkyl group.

Non limitative examples of cyclic fluorocompounds of formula (V) arenotably:

According to a second variant of this preferred embodiment, the cyclicfluorocompound complies with formula (VI) here below:

wherein X″₁ and X″₂, equal to or different from each other, areindependently a fluorine atom, a —R′_(f) group or —OR′_(f) group,wherein R′_(f) is a C₁₋₃ perfluoroalkyl group, and R_(F) and X_(a) havethe same meanings as above defined.

Cyclic fluorocompound of formula (VI) can be prepared by adding to acyclic fluoroolefin a hydrocarbon primary alcohol for obtaining a cyclicfluorinated alcohol derivative, as sketched in the scheme herein below:

wherein X″₁, X″₂ and R_(F) have the meaning as above defined and R′_(H)is H or a C₁₋₆ hydrocarbon group.

Suitable hydrocarbon alcohols include aliphatic alcohols such as lowerprimary alkanols having 1 to 4 carbon atoms. Specific examples includemethanol, ethanol, propanol and butanol, methanol being particularlypreferred.

The reaction of the fluorinated olefin with the alcohol may be carriedout as described in CHAMBERS, R. D. Fluorine in Organic Chemistry.Oxford (UK): Blackwell Publishing, 2004. ISBN 0849317908. p. 199 and ss.

The resulting cyclic fluorinated alcohol derivative can be chemicallyoxidized with an oxidizing agent to the corresponding carboxylic acidderivative (optionally followed by suitable hydrolysis/neutralisationsteps as depicted here below:

wherein X″₁, X″₂, R′_(H), R_(F) and X_(a) have the same meanings asabove defined.

Examples of oxidizing agents include for example potassium permanganate,chromium (VI) oxide, RuO₄ or OsO₄ optionally in the presence of NaOCl,nitric acid/iron catalyst, dinitrogen tetroxide. Typically the oxidationis carried out in acidic or basic conditions, preferably basicconditions, at a temperature between 10° and 100° C. In addition tochemical oxidation, electrochemical oxidation may be used as well.

The cyclic fluorocompound (VI) of the second variant of this preferredembodiment more preferably complies with formula (VII):

wherein X″₁, X″₂, X″₃, X″₄, equal to or different from each other areindependently a fluorine atom, —R′_(f) or —OR′_(f), wherein R′_(f) is aC₁₋₃ perfluoroalkyl group.

Non limitative examples of cyclic fluorocompounds of formula (VII) arenotably:

According to a second embodiment of the invention, the cyclicfluorocompound complies with formula (VIII) here below:

wherein R^(F) and X_(a) have the same meanings as above detailed; X*₁,X*₂ equal to or different from each other are independently a fluorineatom, —R′_(f) or —OR′_(f), wherein R′_(f) is a C₁₋₃ perfluoroalkylgroup; R^(F) ₁ is F or CF₃, k is an integer from 1 to 3.

Compounds of formula (VIII) can be notably manufactured by reaction ofan unsaturated fluorodioxole with a hydrogenated glycol derivative, assketched herein below, so as to obtain a mono-addition compound offormula (X):

wherein X*₁, X*₂, R_(F), k have the same meaning as above defined; R^(H)₁ is H or —CH₃.

Basic catalysis is generally adopted for favouring this reaction.Addition of the hydrogenated glycol derivative is generally carried outusing 1 eq of said unsaturated dioxole (IX) per equivalent of base insaid glycol, so as to maximize yield towards target mono-additioncompound (X). As the hydroxyl functionality is generally unstable underfluorination conditions, the free hydroxyl group of the addition product(X) is generally protected before full fluorination:

wherein X*₁, X*₂, R_(F), R^(H) ₁, k have the meaning above defined; andround circle P denotes a protecting group.

The choice of the protecting agent is not particularly limited, providedthat this group is stable under fluorination conditions. Generally, anesterification with a (per)fluorinated acyl fluoride will be thepreferred route. As an alternative, reaction with any of carbonyldifluoride, carbonyl fluoride bromide and carbonyl fluoride chloride(preferably with carbonyl difluoride) can be performed on compound (X)so as to protect hydroxyl group as fluoroformate group, which isadvantageously stable during fluorination.

The protected addition product (XI) (e.g. under the form of an ester ora fluoroformate) is then fluorinated according to standard procedures,typically using elemental fluorine, to yield correspondingperfluorocompound (XII):

wherein X*₁, X*₂, R_(F), R^(H) ₁, R^(F) ₁, k and round circle P havesame meaning as above detailed.

Said perfluorocompound derivative (XII) is then submitted to appropriatereaction conditions for decomposing/hydrolyzing protecting group of thehydroxyl function, so as to yield corresponding acyl fluoride which isthen converted by hydrolysis/neutralization in target compound (VIII):

wherein X*₁, X*₂, R_(F), R^(F) ₁, X_(a), k and round circle P have samemeaning as above detailed.

This synthetic pathway can be notably applied with success forconverting unsaturated perfluorodioxoles of formulae:

in corresponding cyclic fluorocompounds (VIII) by reaction with ethyleneglycol, reaction with a fluoroacyl compound (e.g. (CF₃)₂—CF—COF) toyield corresponding ester or reaction with a carbonyl fluoride (e.g.COF₂) to yield corresponding fluoroformate, fluorination to yieldcorresponding perfluoroester or perfluoroformate, decomposition of saidperfluoroester or perfluoroformate and final hydrolysis/neutralization,as sketched in following scheme:

wherein X_(a) has the same meaning as above defined. It is alsounderstood that other acyl fluorides than (CF₃)₂CFCOF or other carbonylfluorides other than COF₂ can be used for protecting hydroxyl moiety,such as e.g. CF₃COF.

Perfluoroester and/or perfluoroformate can be notably broken to yieldthe corresponding acyl fluoride by thermal decomposition in the presenceof a nucleophile or an electrophyle, typically in the presence of ametal fluoride of formula MeF_(y), with Me being a metal having yvalence, y being 1 or 2, in particular in the presence of NaF, CaF₂,AgF, CsF, KF, preferably KF.

Otherwise, perfluoroester and/or perfluoroformate can be hydrolyzed inaqueous medium, generally in the presence of suitable HF absorber, e.g.KF, which is known to capture HF yielding KHF₂ in aqueous medium.

Among these compounds, cyclic fluorocompound of formula (XIII), sketchedhere below:

wherein X_(a) has the meaning above defined, has been found particularlyuseful in the process of the invention.

More generally, synthetic approach detailed herein above for secondembodiment of the invention, can be successfully applied for yieldingcyclic fluorocompounds complying with formula (XIV) here below, whichconstitute a further embodiment of the invention:

wherein R_(F) and X_(a) have the same meanings as above detailed; X*₁,X*₂ equal to or different from each other are independently a fluorineatom, —R′_(f) or —OR′_(f), wherein R′_(f) is a C₁₋₃ perfluoroalkylgroup; R*_(F) is a divalent fluorinated group, k is an integer from 1 to3.

Compounds of formula (XIV) can be manufactured following similar pathwayas above detailed for compounds of formula (VIII) by reaction of anunsaturated fluorodioxole with a hydrogenated diol derivative, providedthat such diol comprises at least one —CH₂OH moiety, as sketched hereinbelow, so as to obtain a mono-addition compound of formula (VX):

wherein X*₁, X*₂, R_(F), k have the same meaning as above defined;R*_(H) is a divalent hydrogenated group.

Protection of hydroxyl functionality and fluorination, followed bydecomposing/hydrolyzing protecting group of the hydroxyl function, so asto yield corresponding acyl fluoride, and finalhydrolysis/neutralization in target compound (XIV) can be carried out asabove detailed for compounds (VIII):

wherein X*₁, X*₂, R_(F), R*_(F), R*_(H), k have the meaning abovedefined; and round circle P denotes a protecting group.

The choice of the protecting agent is not particularly limited, providedthat this group is stable under fluorination conditions. Generally, anesterification with a (per)fluorinated acyl fluoride or formation offluoroformate with a carbonyl fluoride will be the preferred routes.

This synthetic pathway can be notably applied with success forconverting unsaturated perfluorodioxole of formulae:

in corresponding cyclic fluorocompounds (XIV) by reaction with differentdiols, like, notably propylene glycol, reaction with a fluoroacylcompound (e.g. CF₃—COF) to yield corresponding ester or reaction with acarbonyl fluoride (e.g. COF₂) to yield corresponding fluoroformate,fluorination to yield corresponding perfluoroester, decomposition ofsaid perfluoroester or perfluoroformate and finalhydrolysis/neutralization, as sketched in following scheme:

Among these compounds, cyclic fluorocompound of formula (XVIII),sketched here below:

wherein X_(a) has the meaning above defined, has been found particularlyuseful in the process of the invention.

In the process of the invention, one or more cyclic fluorocompound offormula (I) are used in the aqueous emulsion polymerization of one ormore fluorinated monomers, in particular gaseous fluorinated monomers.

By gaseous fluorinated monomers is meant monomers that are present as agas under the polymerization conditions. In a particular embodiment, thepolymerization of the fluorinated monomers is started in the presence ofthe cyclic fluorocompound of formula (I), i.e. the polymerization isinitiated in the presence of the same. The amount of cyclicfluorocompound of formula (I) used may vary depending on desiredproperties such as amount of solids, particle size etc. . . . Generallythe amount of cyclic fluorocompound of formula (I) will be between0.001% by weight based on the weight of water in the polymerization and5% by weight. A practical range is between 0.05% by weight and 1% byweight.

While the polymerization is generally initiated in the presence of thecyclic fluorocompound of formula (I), it is not excluded to add furthercyclic fluorocompound of formula (I) during the polymerization, althoughsuch will generally not be necessary.

Nevertheless, it may be desirable to add certain monomer to thepolymerization in the form of an aqueous emulsion. For example,fluorinated monomers and in particular perfluorinated co-monomers thatare liquid under the polymerization conditions may be advantageouslyadded in the form of an aqueous emulsion. Such emulsion of suchco-monomers is preferably prepared using cyclic fluorocompound offormula (I) as an emulsifier.

The aqueous emulsion polymerization may be carried out at a temperaturebetween 10 to 150° C., preferably 20° C. to 130° C. and the pressure istypically between 2 and 50 bar, in particular 5 to 35 bar.

The reaction temperature may be varied during the polymerization e.g.for influencing the molecular weight distribution, i.e., to obtain abroad molecular weight distribution or to obtain a bimodal or multimodalmolecular weight distribution.

The pH of the polymerization media may be in the range of pH 2-11,preferably 3-10, most preferably 4-10.

The aqueous emulsion polymerization is typically initiated by aninitiator including any of the initiators known for initiating a freeradical polymerization of fluorinated monomers. Suitable initiatorsinclude peroxides and azo compounds and redox based initiators. Specificexamples of peroxide initiators include, hydrogen peroxide, sodium orbarium peroxide, diacylperoxides such as diacetylperoxide, disuccinylperoxide, dipropionylperoxide, dibutyrylperoxide, dibenzoylperoxide,di-ter-butyl-peroxide, benzoylacetylperoxide, diglutaric acid peroxideand dilaurylperoxide, and further per-acids and salts thereof such ase.g. ammonium, sodium or potassium salts. Examples of per-acids includeperacetic acid. Esters of the peracid can be used as well and examplesthereof include tert.-butylperoxyacetate and tert.-butylperoxypivalate.Examples of inorganic initiators include for example ammonium-alkali- orearth alkali salts of persulfates, permanganic or manganic acid ormanganic acids. A persulfate initiator, e.g. ammonium persulfate (APS),can be used on its own or may be used in combination with a reducingagent. Suitable reducing agents include bisulfites such as for exampleammonium bisulfite or sodium metabisulfite, thiosulfates such as forexample ammonium, potassium or sodium thiosulfate, hydrazines,azodicarboxylates and azodicarboxyldiamide (ADA). Further reducingagents that may be used include sodium formaldehyde sulfoxylate(Rongalite) or fluoroalkyl sulfinates as disclosed in U.S. Pat. No.5,285,002. The reducing agent typically reduces the half-life time ofthe persulfate initiator. Additionally, a metal salt catalyst such asfor example copper, iron or silver salts may be added. The amount ofinitiator may be between 0.01% by weight (based on the fluoropolymersolids to be produced) and 1% by weight. In one embodiment, the amountof initiator is between 0.05 and 0.5% by weight. In another embodiment,the amount may be between 0.05 and 0.3% by weight.

The aqueous emulsion polymerization can be carried out in the presenceof other materials, such as notably buffers and, if desired,complex-formers or chain-transfer agents.

Examples of chain transfer agents that can be used include dimethylether, methyl t-butyl ether, alkanes having 1 to 5 carbon atoms such asethane, propane and n-pentane, halogenated hydrocarbons such as CCl₄,CHCl₃ and CH₂Cl₂ and hydrofluorocarbon compounds such as CH₂F—CF₃(R134a). Additionally esters like ethylacetate, malonic esters can beeffective as chain transfer agent in the process of the invention.

Examples of fluorinated monomers that may be polymerized using thecyclic fluorocompound according to formula (I) as an emulsifier in theprocess of the invention include partially or fully fluorinated gaseousmonomers including fluorinated olefins such as tetrafluoroethylene(TFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), vinylfluoride (VF), vinylidene fluoride (VDF), partially or fully fluorinatedallyl ethers and partially or fully fluorinated alkyl or alkoxy-vinylethers.

Further, the aqueous emulsion polymerization can be carried out in thepresence of fluorinated fluids, typically enabling formation ofnanosized droplets (average size of less than 50 nm, preferably of lessthan 30 nm) stabilized in aqueous dispersion by the presence of thecyclic fluorocompound of formula (I).

Should the process of the invention be carried out in the presence of afluorinated fluid, as above detailed, it may be preferable to firsthomogenously mix cyclic compound and said fluid in aqueous phase,possibly in an aqueous medium, and then feeding an aqueous mixture ofcompound (I) and said fluid in the polymerization medium. This techniqueis particularly advantageous as this pre-mix can advantageously enablemanufacture of an emulsion of said fluid in an aqueous phase comprisingthe cyclic compound, wherein this emulsion comprises dispersed dropletsof said fluid having an average size of preferably less than 50 nm, morepreferably of less than 40 nm, even more preferably of less than 30 nm.

Fluids which can be used according to this embodiment are preferably(per)fluoropolyethers comprising recurring units (R1), said recurringunits comprising at least one ether linkage in the main chain and atleast one fluorine atom (fluoropolyoxyalkene chain). Preferably therecurring units R1 of the (per)fluoropolyether are selected from thegroup consisting of:

(I) —CFX—O—, wherein X is —F or —CF₃; and(II) —CF₂—CFX—O—, wherein X is —F or —CF₃; and

(III) —CF₂—CF₂—CF₂—O—; and (IV) —CF₂—CF₂—CF₂—CF₂—O—; and

(V) —(CF₂)_(j)—CFZ—O— wherein j is an integer chosen from 0 and 1 and Zis a fluoropolyoxyalkene chain comprising from 1 to 10 recurring unitschosen among the classes (I) to (IV) here above; and mixtures thereof.

Should the (per)fluoropolyether comprise recurring units R1 of differenttypes, advantageously said recurring units are randomly distributedalong the fluoropolyoxyalkene chain.

Preferably the (per)fluoropolyether is a compound complying with formula(I-p) here below:

T₁-(CFX)_(p)—O—R_(f)—(CFX)_(p′)-T₂  (I-p)

wherein:

-   -   each of X is independently F or CF₃;    -   p and p′, equal to or different from each other, are integers        from 0 to 3;    -   R_(f) is a fluoropolyoxyalkene chain comprising repeating units        R^(o), said repeating units being chosen among the group        consisting of:        (i) —CFXO—, wherein X is F or CF₃,        (ii) —CF₂CFXO—, wherein X is F or CF₃,        (iii) —CF₂CF₂CF₂O—,

(iv) —CF₂CF₂CF₂CF₂O—,

(v) —(CF₂)_(j)—CFZ—O— wherein j is an integer chosen from 0 and 1 and Zis a group of general formula —OR_(f)′T₃, wherein R_(f)′ is afluoropolyoxyalkene chain comprising a number of repeating units from 0to 10, said recurring units being chosen among the followings: —CFXO—,—CF₂CFXO—, —CF₂CF₂CF₂O—, —CF₂CF₂CF₂CF₂O—, with each of each of X beingindependently F or CF₃; and T₃ is a C₁-C₃ perfluoroalkyl group, andmixtures thereof;

-   -   T₁ and T₂, the same or different from each other, are H, halogen        atoms, C₁-C₃ fluoroalkyl groups, optionally comprising one or        more H or halogen atoms different from fluorine.

The polymerization may further involve non-fluorinated monomers such asethylene and propylene.

Further examples of fluorinated monomer that may be used in the aqueousemulsion polymerization according to the invention include thosecorresponding to the formula: CF₂═CF—O—R_(f) wherein R_(f) represents aperfluorinated aliphatic group that may contain one or more oxygenatoms.

Still further, the polymerization may involve comonomers that have afunctional group such as for example a group capable of participating ina peroxide cure reaction. Such functional groups include halogens suchas Br or I as well as nitrile groups.

The aqueous emulsion polymerization may be used to produce a variety offluoropolymers including perfluoropolymers, which have a fullyfluorinated backbone, as well as partially fluorinated fluoropolymers.Also the aqueous emulsion polymerization may result in melt-processablefluoropolymers as well as those that are not melt-processable such asfor example polytetrafluoroethylene and so-called modifiedpolytetrafluoroethylene. The polymerization process can further yieldfluoropolymers that can be cured to make fluoroelastomers as well asfluorothermoplasts. Fluorothermoplasts are generally fluoropolymers thathave a distinct and well noticeable melting point, typically in therange of 60 to 320° C. or between 100 and 320° C. They thus have asubstantial crystalline phase. Fluoropolymers that are used for makingfluoroelastomers typically are amorphous and/or have a negligible amountof crystallinity such that no or hardly any melting point is discernablefor these fluoropolymers.

According to an embodiment of the method of the invention, the methodcomprises polymerizing in aqueous emulsion in the presence of a mixtureof the cyclic fluorocompound of formula (I) and at least one furtheremulsifier different from cyclic fluorocompound of formula (I).

The choice of said additional emulsifier is not particularly limited.Generally fluorinated emulsifiers will be used in combination withcyclic fluorocompound of formula (I).

More specifically, fluorinated emulsifier [surfactant (FS)] of formula:

R_(f§)(X⁻)_(j)(M⁺)_(j)

wherein R_(f§) is a C₃-C₃₀ (per)fluoroalkyl chain,(per)fluoro(poly)oxyalkylenic chain, X⁻ is —COO⁻, —PO₃ ⁻ or —SO₃ ⁻, M⁺is selected from H⁺, NH₄ ⁺, an alkaline metal ion and j can be 1 or 2.

As non limitative example of surfactants (FS), mention may be made ofammonium and/or sodium perfluorocarboxylates, and/or(per)fluoropolyoxyalkylenes having one or more carboxylic end groups.

Other examples of fluorinated surfactants are (per)fluorooxyalkylenicsurfactants described in US 2007015864 (3M INNOVATIVE PROPERTIES) Aug.1, 2007, US 2007015865 (3M INNOVATIVE PROPERTIES CO) 18 Jan. 2007, US2007015866 (3M INNOVATIVE PROPERTIES CO) 18 Jan. 2007, US 2007025902 (3MINNOVATIVE PROPERTIES CO) Jan. 2, 2007.

More preferably, the fluorinated emulsifier [surfactant (FS)] is chosenfrom:

-   -   CF₃(CF₂)_(n1)COOM′, in which n₁ is an integer ranging from 4 to        10, preferably from 5 to 7, and more preferably being equal to        6; M′ represents H, NH₄, Na, Li or K, preferably NH₄;    -   T(C₃F₆O)_(n0)(CFXO)_(m0)CF₂COOM″, in which T represents Cl or a        perfluoroalkoxyde group of formula C_(k)F_(2k+1)O with k is an        integer from 1 to 3, one F atom being optionally substituted by        a Cl atom; no is an integer ranging from 1 to 6; m₀ is an        integer ranging from 0 to 6; M″ represents H, NH₄, Na, Li or K;        X represents F or CF₃;    -   F—(CF₂—CF₂)_(n2)—CH₂—CH₂—RO₃M′″, in which R is P or S,        preferably S, M′″ represents H, NH₄, Na, Li or K, preferably H;        n₂ is an integer ranging from 2 to 5, preferably n2=3;    -   A-R_(f)—B bifunctional fluorinated surfactants, in which A and        B, equal to or different from each other, are —(O)_(p)CFX—COOM*;        M* represents H, NH₄, Na, Li or K, preferably M* represents NH₄;        X═F or CF₃; p is an integer equal to 0 or 1; R_(f) is a linear        or branched perfluoroalkyl chain, or a (per)fluoropolyether        chain such that the number average molecular weight of A-R_(f)—B        is in the range 300 to 3,000, preferably from 500 to 2,000;    -   R′_(f)—O—(CF₂)_(r)—O-L-COOM′, wherein R′_(f) is a linear or        branched perfluoroalkyl chain, optionally comprising catenary        oxygen atoms, M′ is H, NH₄, Na, Li or K, preferably M′        represents NH₄; r is 1 to 3; L is a bivalent fluorinated        bridging group, preferably —CF₂CF₂— or —CFX—, X═F or CF₃;        R″_(f)—(OCF₂)_(u)—O—(CF₂)_(v)—COOM″, wherein R″_(f) is a linear        or branched perfluoroalkyl chain, optionally comprising catenary        oxygen atoms, M″ is H, NH₄, Na, Li or K, preferably M″        represents NH₄; u and v are integers from 1 to 3;    -   R′″_(f)—(O)_(t)—CHQ-L-COOM′″, wherein R′″_(f) is a linear or        branched perfluoroalkyl chain, optionally comprising catenary        oxygen atoms, Q=F or CF₃, t is 0 or 1, M′″ is H, NH₄, Na, Li or        K, preferably M′″ is NH₄; L is a bivalent fluorinated bridging        group, preferably —CF₂CF₂— or —CFX—, X═F or CF₃;    -   and mixtures thereof.

Particular good results have been obtained with mixtures of compound (I)with A-R_(f)—B bifunctional fluorinated surfactants; said bifunctionalsurfactant A-R_(f)—B preferably complies with formulaM₂OOC—CFX_(z)—O—R_(fz)—CFX_(z)—COOM_(z),

wherein M_(z) is H, NH₄, Na, Li or K, preferably M_(z) is NH₄; X_(z)═F,—CF₃; R_(tz) is a (per)fluoropolyether chain comprising recurring unitscomplying with one or more of formulae: —(C₃F₆O)—; —(CF₂CF₂O)—;—(CFL_(O)O)—, wherein L₀=F, —CF₃; —(CF₂(CF₂)_(z′)CF₂O)—, wherein z′ is 1or 2; —(CH₂CF₂CF₂O)—.

R_(fz) preferably has one of the following structures:

1) —(CF₂O)_(a)—(CF₂CF₂O)_(b)—

wherein a and b≧0; should a and b be simultaneously >0, b/a ratio isgenerally comprised between 0.01 and 10, extremes included;2) —(CF₂—(CF₂)_(z′)—CF₂O)_(b′)—, with b′>0 and z′ being 1 or 2;3) —(C₃F₆O)_(r)—(C₂F₄O)_(b)—(CFL₀O)_(t)—, wherein r, b and t≧0, L₀=F,—CF₃; should r, b and t be simultaneously >0, r/b ratio is typicallycomprised in the range 0.5-2.0 and (r+b)/t in the range 10-30;4) —(OC₃F₆)_(r)—(OCFL₀)_(t)-OCF₂—R*_(f)—CF₂O—(C₃F₆O)_(r)—(CFL₀O)_(t)—,wherein R*_(f) is a fluoroalkylene group from 1 to 4 carbon atoms; L₀=F,—CF₃; r, t being ≧0.

Most preferred A-R_(f)—B bifunctional fluorinated surfactant complieswith formulaM_(z)OOC—CFX_(z)—O—(CF₂O)_(a)—(CF₂CF₂O)_(b)—CFX_(z)—COOM_(z), whereinM_(z) is H, NH₄, Na, Li or K, preferably M_(z) is NH₄; X_(z)═F, —CF₃;and a, b, both >0, are selected so that b/a is comprised between 0.3 and10 and the molecular weight of the surfactant is comprised between 500and 2000.

Should the process of the invention be carried out in the presence ofmixture of cyclic compound and further fluorinated emulsifier, as abovedetailed, it may be preferable to first homogenously mix cyclic compoundand further emulsifier in aqueous phase, and then feeding an aqueousmixture of compound (I) and said emulsifier in the polymerizationmedium. This technique is particularly advantageous when the furtherfluorinated emulsifier is poorly soluble in water. Thus, this pre-mixcan advantageously enable manufacture of an emulsion of said fluorinatedemulsifier in an aqueous phase comprising the cyclic compound, whereinthis emulsion comprises dispersed droplets of said fluorinatedemulsifier having an average size of preferably less than 50 nm,preferably of less than 40 nm, more preferably of less than 30 nm.

Further, in addition, the aqueous emulsion polymerization of thisembodiment can be carried out in the presence of fluorinated fluids, asabove referred, typically enabling formation of nanosized droplets(average size of less than 50 nm, preferably of less than 30 nm)stabilized in aqueous dispersion by the presence of the mixture of thecyclic fluorocompound of formula (I) and at least one further emulsifierdifferent from cyclic fluorocompound of formula (I).

Fluorinated fluids which can be used in combination with said mixture ofcompound (I) and emulsifier are those above referred, suitable for beingused in combination with the cyclic fluorocompound of formula (I).

The aqueous emulsion polymerization process of the invention results ina dispersion of the fluoropolymer in water comprising the cyclicfluorocompound of formula (I). Generally the amount of solids of thefluoropolymer in the dispersion directly resulting from thepolymerization will vary between 3% by weight and about 40% by weightdepending on the polymerization conditions. A typical range is between 5and 30% by weight, for example between 10 and 25% by weight.

The particle size (volume average diameter) of the fluoropolymer istypically between 40 nm and 400 nm with a typical particle size between60 nm and about 350 nm being preferred. The total amount of cyclicfluorocompound formula (I) in the resulting dispersion is typicallybetween 0.001 and 5% by weight based on the amount of fluoropolymersolids in the dispersion. A typical amount may be from 0.01 to 2% byweight or from 0.02 to 1% by weight.

The fluoropolymer may be isolated from the dispersion by coagulation ifa polymer in solid form is desired. Also, depending on the requirementsof the application in which the fluoropolymer is to be used, thefluoropolymer may be post-fluorinated so as to convert any thermallyunstable end groups into stable CF₃— end groups.

For coating applications, an aqueous dispersion of the fluoropolymer isdesired and hence the fluoropolymer will not need to be separated orcoagulated from the dispersion. To obtain a fluoropolymer dispersionsuitable for use in coating applications such as for example in theimpregnation of fabrics or in the coating of metal substrates to makefor example cookware, it will generally be desired to add furtherstabilizing surfactants and/or to further increase the fluoropolymersolids. For example, non-ionic stabilizing surfactants may be added tothe fluoropolymer dispersion. Typically these will be added thereto inan amount of 1 to 12% by weight based on fluoropolymer solids. Examplesof non-ionic surfactants that may be added includeR¹—O—[CH₂CH₂O]_(n)—[R²O]_(m)—R³ (NS) wherein R¹ represents an aromaticor aliphatic hydrocarbon group having from 6 to 18 carbon atoms, R²represents an alkylene having 3 carbon atoms, R³ represents hydrogen ora C₁₋₃ alkyl group, n has a value of 0 to 40, m has a value of 0 to 40and the sum of n+m being at least 2. It will be understood that in theabove formula (NS), the units indexed by n and m may appear as blocks orthey may be present in an alternating or random configuration. Examplesof non-ionic surfactants according to formula (VI) above includealkylphenol oxy ethylates such as ethoxylated p-isooctylphenolcommercially available under the brand name TRITON™ such as for exampleTRITON™ X 100 wherein the number of ethoxy units is about 10 or TRITON™X 114 wherein the number of ethoxy units is about 7 to 8. Still furtherexamples include those in which R¹ in the above formula (NS) representsan alkyl group of 4 to 20 carbon atoms, m is 0 and R³ is hydrogen. Anexample thereof includes isotridecanol ethoxylated with about 8 ethoxygroups and which is commercially available as GENAPOL® X080 fromClariant GmbH. Non-ionic surfactants according to formula (NS) in whichthe hydrophilic part comprises a block-copolymer of ethoxy groups andpropoxy groups may be used as well. Such non-ionic surfactants arecommercially available from Clariant GmbH under the trade designationGENAPOL® PF 40 and GENAPOL® PF 80.

The amount of fluoropolymer solids in the dispersion may beupconcentrated as needed or desired to an amount between 30 and 70% byweight. Any of the known upconcentration techniques may be usedincluding ultrafiltration and thermal upconcentration.

Still an object of the invention are fluoropolymer dispersionscomprising at least one cyclic fluorocompound of formula (I), as abovedescribed.

Said fluoropolymer dispersions are typically obtained by the process ofthe invention.

Concentration of cyclic fluorocompound of formula (I) in thefluoropolymer dispersions of the invention can be reduced, if necessary,following traditional techniques. Mention can be made of ultrafiltrationcombined with percolate recycle, as described in U.S. Pat. No. 4,369,266(HOECHST AG) 18 Jan. 1983, treatment with ion exchange resins in thepresence of a non-ionic surfactant (as described in EP 1155055 A (DYNEONGMBH) 21 Nov. 2001), of an anionic surfactant (as exemplified in EP1676868 A (SOLVAY SOLEXIS SPA) May 7, 2006) or of a polyelectrolyte (astaught in EP 1676867 A (SOLVAY SOLEXIS SPA) May 7, 2006).

The invention thus also pertains to a process for recovering cyclicfluorocompound of formula (I) from fluoropolymer dispersions comprisingthe same. The process preferably comprises contacting the fluoropolymerdispersion with a solid adsorbing material, typically an ion exchangeresin, preferably an anion exchange resin: the cyclic fluorocompound offormula (I) is advantageously adsorbed (at least partially) onto thesolid adsorbing material. Cyclic fluorocompound of formula (I) can beefficiently recovered from solid adsorbing material by standardtechnique, including elution, thermal desorption and the like. In caseof elution, in particular from anion exchange resin, cyclicfluorocompound of formula (I) can be recovered by elution with an acidicsolution. Typically, an aqueous medium comprising an acid and awater-miscible organic solvent can be used to this aim. Mixtures ofinorganic acid and alcohol in water are particularly effective. Cyclicfluorocompound (I) can be notably recovered from such liquid phases bystandard methods, including, notably crystallization, distillation (e.g.under the form of ester) and the like.

Also, cyclic fluorocompound (I) as above detailed and processes for itsmanufacture are other objects of the present invention.

The invention will be now explained in more detail with reference to thefollowing examples, whose purpose is merely illustrative and notintended to limit the scope of the invention.

Preparative Example 1 Synthesis of Compound VIIa (with X_(a)═NH₄)Example 1a Reaction Between Perfluoro-5-Methoxy-1,3-Dioxole (MDO, (A) inScheme Here Below) and Methanol

CaCO₃ (7.14 mmol, 0.714 g) was introduced in a stainless steel highpressure vessel equipped with a digital manometer and a magneticstirrer. After careful evacuation at room temperature, a mixtureconsisting of CH₃OH (3.57 moles, 114 g), di-tert-butyl peroxide (DTBP;71.4 mmol, 10.5 g) and MDO (0.714 mol, 150 g) was introduced into thevessel. The vessel was then heated at 134° C. under vigorous stirringfor 21 hours, by monitoring internal pressure. Once the reactioncompleted, the vessel was cooled to room temperature and the crudereaction mixture was recovered and rinsed several times with distilledwater. The organic (lower) phase is first dried over MgSO₄, filtered andfinally distilled. Isolated yield=56% with respect to the starting MDO(A). b.p.=142° C. Selectivity=95% towards target isomer (B); 5% towardsalternative isomer (C). FIG. 1 depicts the ¹⁹F-NMR spectrum recorded oncompound (B).

Example 1b Oxidation of Alcohol Intermediate (B)

An aqueous solution composed of KMnO₄ (238 mmol, 37.6 g), NaOH (238mmol, 9.52 g) in 200 ml of distilled H₂O was introduced in a 3-neckedglass round-bottomed flask equipped with a magnetic stirrer, a droppingfunnel, a thermometer and a tap water refrigerating column. The flaskwas heated to 80° C. with vigorous stirring and then 238 mmol; 50 g ofproduct obtained from step 1a was slowly dropped into the basicoxidizing solution. Immediate exothermic release (+15° C.) was observedtogether with formation of MnO₂ precipitate. After completion of theaddition, solution was further stirred at 80° C. for 40 min. Crudereaction mixture was then cooled to room temperature, filtered,acidified to pH=1 with concentrated HCl (37% w/w) and extracted severaltimes with CH₂Cl₂. The organic layer was dried over MgSO₄, filtered andthen the CH₂Cl₂ is evaporated. Isolated yield=55%, conversion of productfrom 1a=100%. pK_(a) of (D)=2.8.

Example 1c Synthesis of VIIa by Basic Hydrolysis of Acid (D)

An organic solution composed of (D) (127 mmol; 30.6 g) and 200 ml ofCH₂Cl₂ was introduced in a 2-necked glass round-bottomed flask equippedwith a magnetic stirrer, a tap water refrigerating column and a bubblingtube. The mixture was cooled to 0° C. with vigorous stirring and a largeexcess of gaseous NH₃ was bubbled through the organic mixture. Bubblingof NH₃ (g) was pursued until completion of the precipitation of theammonium salt. Crude mixture was filtered; solid was dried in a vacuumoven at 40° C. under reduced pressure (20 mmHg) for 2 hours. A flakywhite solid is obtained. Isolated yield of compound (E) (VIIa, withX_(a) being NH₄)=100%. The thermogravimetric analysis (TGA) in airpoints out a weight decrease of 10% at 148° C. and of 50% at 182° C.FIG. 2 depicts the ¹⁹F-NMR spectrum of compound (E). LC-MS analysisshowed a strong peak at m/z=255 (corresponding to the carboxylate mieutyof (E)). The oral acute toxicity of compound VIIa was evaluatedaccording to standard practice; LD₅₀ was found to exceed 2000 mg/kg.

Preparative Example 2 Synthesis of Compound Va (with X_(a)═NH₄) Example2b Esterification of Alcohol Intermediate (B)

Alcohol intermediate (B) (333 mmol, 70 g) obtained from example 1a wasmade to react with CF₃COF (350 mmol, 40.5 g) in 200 ml of A113 at T=0°C. Solvent and unreacted CF₃COF were removed by distillation at 40°C./600 mm Hg.

Example 2c Fluorination of Ester (F)

Ester (F) was diluted in A113 (200 ml) and fluorinated with a mixtureF₂/N₂ (20/80) at a temperature of 0 to 10° C. Reaction was monitored bygas chromatography. Once fluorination completed, residual F₂ was ventedby bubbling a flow of nitrogen. Perfluoroester (G) was recovered afterremoval under reduced pressure of solvent.

Example 2d Hydrolysis of Perfluorinated Ester (G)

Perfluorinated ester (G) was hydrolyzed in water at 0° C., yieldingcorresponding acid with quantitative yield. Evolved HF was neutralizedwith 1.5 mol eq. of KF, yielding solid KHF₂, which was separated byfiltration. After removal of solvent, the free acid (b.p.=160° C.) andCF₃COOH (b.p.=72° C.) were separated by fractional distillation. GaseousNH₃ was then bubbled in a CH₂Cl₂ (200 ml) solution of the acid; ammoniumsalt (H) (formula Va, with X_(a)═NH₄) was then recovered with a yield of75% moles (with respect to alcohol intermediate (B)). Thethermogravimetric analysis (TGA) in Air points out a weight decrease of10% at 145° C. and of 50% at 182° C. FIG. 3 depicts the ¹⁹F-NMR spectrumrecorded on compound (H).

Example 2e Preparation of Fluoroformate of Alcohol Intermediate (B)

In a 250 ml stainless steel reactor equipped with mechanic stirrer, gasinlet, gas outlet, a thermocouple to check the internal temperature, andexternal cooling bath, 99 g of a alcohol of the above formula (B) and 34g of powdered NaF were loaded and the external temperature set at 15° C.Then, COF₂ (2.0 Nl/h obtained by reaction between 2.5 Nl/h of CO and 2.0Nl/h of F₂) diluted with 1.0 Nl/h of He were introduced into the reactorkept under vigorous stirring. The off-gases were analysed by a G.C.system to evaluate COF₂ conversion. After 6.0 hours feeding was stoppedand crude mixture was filtered to separate inorganic salts. The liquidproduct was analyzed by ¹⁹F NMR showing an almost quantitativeconversion of the starting alcohol and selectivity in the desiredfluoroformate.

Example 2f Fluorination of Fluoroformate (F′)

In a 250 ml stainless steel reactor equipped with mechanic stirrer, twogas inlets, one gas outlet, a thermocouple to check the internaltemperature, and external cooling bath, 81 g of the fluoroformate offormula (F′) were introduced and fluorinated according to the sameprocedure of Example 1, with the exception that F₂ was fed at 1.8 Nl/h,diluted with 3.0 Nl/h of He. After 15 hours, the internal temperaturefell quickly from 5° C. to 0° C., and no additional F₂ conversion wasobserved. The crude mixture was collected and analyzed by GC and ¹⁹FNMR. The desired perfluorofluoroformate (G′) was obtained with about 96%yield.

Example 2g Hydrolysis of Perfluoroformate (G′)

Same procedure as detailed in example 2d was followed.

Determination of surface tension of aqueous solution of compounds Va andVIIa (with X_(a)═NH₄)

Surface tension measurements have been carried out on diluted solutionsof ammonium salts of compounds (Va) and (VIIa) in water at a temperatureof 25° C., using a LAUDA TE1C tensiometer equipped with a Pt ring; rawdata have been worked up with Huh-Mason technique. For comparisonpurposes, surface tension has been also determined in same conditions onwater solution of ammonium perfluorooctanoate (APFO). A sketch of thesurface tension (in mN/m) as a function of concentration (in g/l) forcompounds Va, VIIa and APFO is given in FIG. 4.

Simulation Using Density Functional Theory for Prediction ofBiopersistence Behaviour of Compound Va

Using density functional theory, minimum energy conformational structureof carboxylated anion of compound (Va) either in vacuum or in aqueoussolution have been determined; in particular, volume and surface of themolecule in solution, solvatation free energy, length of main chain ofthe molecule, vibrational entropy, equivalent diameter, electricalcharges at the oxygen and carbon atoms of the carboxylic groups, dipolemomentum have been determined.

Structural and energetic data have been also calculated as abovedescribed for several fluorosurfactants such as perfluorooctanoate andother compounds having catenary oxygen atoms, for which biopersistencedata were available, So as to establish appropriate correlations amongsaid data and biopersistence profile. In particular, the ratio betweensolvatation free energy and the length of the molecule has been found todirectly correlate to the fraction (%) of compound eliminated from aliving animal in rats after 96 hours from administration, as determinedby urine analysis.

On the basis of said relation, it has been possible to determine arecovery/elimination for cyclic compound of formula (Va) exceeding 95%after 96 hours from administration, while only 5% are expected to berejected from living body from similar calculations fromperfluorooctanoate. These data well demonstrate that the cycliccompounds of the invention indeed possess a more favourablebiopersistence profile over traditional fluorosurfactants.

Blood and Urine Levels and Pharmacokinetic Parameters of Compounds Vaand VIIa (X_(a)═NH₄)

Compound Va and VIIa (X_(a)═NH₄) were administered by single oral route(gavage) three male Wistar (SPF-bred) rats at dose levels of about 70μmol/kg of dry ammonium salt, corresponding to the 21.2 mg/kg forcompound Va and 19.9 mg/kg for compound VIIa. Blood sampling occurred 15minutes before administration, at 4, 8, 12, 24, 72 and 168 hours afteradministration. For compound Va, maximal plasma concentrations (C_(max))was observed at 4 h (t_(max)) with a reliable plasma half life of3.1-4.5 hours after oral administration. For compound VIIa, maximalplasma concentrations (C_(max)) was also observed at 4 h (t_(max)) witha reliable plasma half life of 8.0-8.9 hours. The PK parameters of thesecompounds after single oral (gavage) administration to male rats aresummarized in the table below:

TABLE 1 Parameter Va (X_(a) = NH₄) VIIa (X_(a) = NH₄) Dose [mg/g] 21.219.9 Males group (plasma) C_(max) [ng/mL] 22997, 14997, 11258, 14767,24345 18878 t_(max) [h] 4, 4, 4 4, 4, 4 AUC_(0-t) [ng · h/mL] 135856,68016, 47070, 114562, 118024 135608 AUC_(inf.) [ng · h/mL] 136026,68289, 47137, 115916, 121185 137788 t_(1/2, z) [h] 4.5, 3.1, 4.0 4.8,8.0, 8.9data relative to the three animals dosed.

Individual and mean urine levels in rats, after single oraladministration, resulted in urinary half lives of 9, 13, 10 hours with arecovery of 97-107% at 168 hours after treatment for compound VIIa;compound Va reported urinary half lives of 15, 11 and 28 hours with arecovery of 80-83% at 168 hours after treatment.

Compound XIII was dosed by single oral administration to 3 male Wistarrats at the dose of 73 umol/kg corresponding to 26.06 mg/kg. Bloodsampling occurred at 15 minutes before administration, at 4, 8, 12, 24,72 and 168 hours after administration. Urine samples were obtained attime intervals 0-12, 12-24, 24-72, 72-96, 96-168 hours after dosing.Plasma and urine concentration of XIII were determined by a validatedanalytical method. The maximum plasma concentration (C_(max)) wasobserved at 4 hours (t_(max)). Mean urinary recovery in 168 hours aftertreatment was around 82%.

Results of plasma concentrations for compound VIIa (X_(a)═NH₄), Va(X_(a)═NH₄), XIII (X_(a)═NH₄) and APFO as a function of time aresketched in FIG. 5. This graph depicts ratio C/C_(max) for compound Va(X_(a)═NH₄) () compound VIIa (X_(a)═NH₄) (O), for compound XIII(X_(a)═NH₄) (□) and APFO (▴), with C=instantaneous plasma concentrationand C_(max)=maximum plasma concentration, as a function of time (inhours). Experimental data indicate significantly faster elimination ofcompound Va, VIIa and XIII (X_(a)═NH₄) from blood after single oraladministration than what observed for APFO. Recoveries from urines forall the 3 compounds exceeded always 80% after 96 and 168 hours fromtreatment.

TGA Analyses of Compounds Va and VIIa (X_(a)═NH₄) and APFO as Comparison

FIG. 6 depicts the TGA traces as % wt loss as a function of temperature(in ° C.) for APFO (1), compound Va (2) and VIIa (X_(a)═NH₄) (3). Thesedata well demonstrate that cyclic compounds are more volatile thatperfluoroalkanoic acids and thus are expected to leave lower levels ofresidues in final parts obtained from dispersions containing the same.

Polymerization Example 3 PTFE Polymerization in the Presence of CompoundVa (X_(a)═NH₄)

A polymerization reactor having a total volume of 100 cc equipped with amechanical stirrer was charged with 60 cc of deionised water, 0.12 g ofcompound Va (X_(a)═NH₄) and 1.0 g of paraffin wax with softening pointcomprised 52° C. and 58° C. The reactor was evacuated and heated up to70° C. The reactor was kept under mechanical stirring and loaded withgaseous TFE until reaching a pressure of 20 barg. The polymerization wasinitiated by a solution containing 0.5 mg of ammonium peroxodisulfate(NH₄)₂S₂O₈ (APS) and 9.6 mg of disuccinic acid peroxide (DSAP). Reactionpressure was maintained at set point of 20 barg by feeding gaseous TFE.The reaction temperature was increased until 80° C. with a rate of 0.5°C./min. After 80 min, feeding of TFE was interrupted, reactor was ventedand cooled. A stable PTFE dispersion having a solid content of 20% wtwas obtained; no coagulum was formed in the reactor duringpolymerization: The latex particle diameter was found to be 235 nm whenmeasured by Laser Light Scattering (LLS).

Preparative Example 4 Synthesis of Compound XIII (with X_(a)═NH₄)Example 4a Reaction Between Perfluoro-5-Methoxy-1,3-Dioxole (MDO, (A) inScheme Here Below) and Ethylene Glycol

In a four necked roundbottomed glass reactor, equipped with magneticstirrer, thermometer, condenser maintained at −75° C. (dry ice-isopropylalcohol) and two addition funnels, 450 g of ethylene glycol wereintroduced; the reactor was cooled to 0° C. in an ice water bath; asolution of 11.4 g (285 meq) of NaOH (s) and 60 ml of distilled waterH₂O was then added in half an hour. After a slight exothermicity, themixture was heated to 80° C.; 150 g (714 mmoli) of MDO were thus slowlyadded. At the end of the addition, reaction mixture was stirred foranother 2 hours. After cooling at 20° C., 250 ml of dichloromethane wereadded and resulting mixture was rinsed twice with brine. The organic(lower) phase was first dried over MgSO₄, filtered and then CH₂Cl₂ wasevaporated. Isolated yield of compound (L) was found to be 74%.

Example 4b Esterification of Alcohol Intermediate (L)

Alcohol intermediate (L) (184 mmol, 50 g) obtained from example 4a wasmade to react with CF₃COF (200 mmol, 23.2 g) in 150 ml of A113 at T=0°C. Solvent and unreacted CF₃COF were removed by distillation at 40°C./600 mm Hg.

Example 4c Fluorination of Ester (M)

Ester (M) was diluted in A113 (150 ml) and fluorinated with a mixtureF₂/N₂ (20/80) at a temperature of 0 to 30° C. Reaction was monitored bygas chromatography. Once fluorination was completed, residual F₂ wasvented by bubbling a flow of nitrogen. Perfluoroester (N) was recoveredafter removal of solvent by fractional distillation.

Example 4d Hydrolysis of Perfluoroester (N)

Perfluorinated ester (N) was hydrolyzed in water at 0° C., yielding thecorresponding acid with quantitative yield. Evolved HF was neutralizedwith 1.5 mol eq. of KF, yielding solid KHF₂, which was separated byfiltration. After removal of solvent, the free acid (XIII, X_(a)═H) andCF₃COOH (b.p.=72° C.) were separated from each other by fractionaldistillation.

Acid (XIII, X_(a)═H) was solubilised in CH₂Cl₂ (200 ml); gaseous NH₃ wasthen bubbled in said solution; ammonium salt (XIII, X_(a)═NH₄) was thenrecovered with a yield of 75% moles (with respect to alcoholintermediate (L)). The thermogravimetric analysis (TGA) in air pointedout a weight decrease of 10% at 159° C. and of 50% at 191° C. FIG. 7depicts the ¹⁹F-NMR spectrum recorded on ammonium salt (XIII,X_(a)═NH₄).

Example 4e Fluoroformate Preparation from of Alcohol Intermediate (L)

In a 500 ml stainless steel reactor equipped with mechanic stirrer, gasinlet, gas outlet, a thermocouple to check the internal temperature, andexternal cooling bath, 393 g of an alcohol of the above formula (L) and92 g of powdered NaF were introduced and the external temperature set at15° C.

Then, COF₂ (6.0 Nl/h obtained by reaction between 7.0 Nl/h of CO and 6.0Nl/h of F₂) diluted with 2.0 Nl/h of He were introduced into the reactorwhile keeping reaction medium under vigorous stirring. The off-gaseswere analysed by a G.C. system to evaluate COF₂ conversion. After 6.75hours feeding was stopped and crude mixture was filtered to separateinorganic salts. The liquid product was analyzed by ¹⁹F NMR showing analmost quantitative conversion of the starting alcohol and selectivityin the desired fluoroformate (M′).

Example 4f Fluorination of Fluoroformate (M′)

In a 500 ml stainless steel reactor equipped with mechanic stirrer, twogas inlets, one gas outlet, a thermocouple to check the internaltemperature, and external cooling bath, 278 g of a fluoroformate of theabove formula (M′) were loaded and the external temperature set at 0° C.Then, two different stream of gases were introduced by the inlets intothe reactor kept under vigorous stirring: F₂ (2.3 Nl/h) diluted with 4.5Nl/h of He, and C₃F₆ (0.3 Nl/h) diluted with 1.5 Nl/h of He. Theoff-gases went through a NaF trap and analyzed by GC to evaluate F₂conversion and thus estimate the C—H to C—F conversion. The internaltemperature remained constant at +5° C. After 57 hours, the internaltemperature fell quickly from 5° C. to 0° C., and no additional F₂conversion was observed. The feeding was stopped and the residual HF wasremoved by inert gas. The crude mixture was collected and analyzed by GCand ¹⁹F NMR. The desired perfluorofluoroformate (N′) was obtained with aroughly 95% yield.

Example 4g Hydrolysis of Perfluoroformate (N′)

Same procedure as detailed in step 4d. was followed.

Determination of Surface Tension of Aqueous Solution of Compound XIII(with X_(a)═NH₄)

Surface tension measurements have been carried out on diluted solutionsof ammonium salts of compound (XIII) as detailed above for (Va) and(VIIa). A sketch of the surface tension (in mN/m) as a function ofconcentration (in g/l) for compound (XIII) is given in FIG. 4.

TGA Analyses of Compounds XIIIa (X_(a)═NH₄) and APFO as Comparison

FIG. 8 depicts the TGA traces as % wt loss as a function of temperature(in ° C.) for APFO (1) and compound XIII (X_(a)═NH₄) (2). These datawell demonstrate that cyclic compound is more volatile thatperfluoroalkanoic acids, possibly via decarboxylation phenomena and thusis expected to leave lower levels of residues in final parts obtainedfrom dispersions containing the same.

Further TGA isothermal scans under vacuum have been carried out oncompound XIII (X_(a)═NH₄) at T=150 and 180° C., for evaluatingdecarboxylation kinetic; these scans are provided in FIG. 9, wherein inabscissa time (in minutes) is given, while other axis provides with the% of weight with respect to initial weight. GC coupled with massspectrometry has enabled identifying in cyclic C₅O₄F₉H (i.e.corresponding decarboxylated compound) largely prevailing volatilematerial detected.

Polymerization Example 5 PTFE Polymerization in the Presence of CompoundXIII (X_(a)═NH₄) and Recovery of Compound XIII (X_(a)═NH₄) by IonExchange

A polymerization reactor having a total volume of 5000 ml equipped witha mechanical stirrer (500 rpm) was charged with 3 l of deionised water,heated at 60° C. and further loaded with 60 g of a 10% wt aqueoussolution of compound XIII (X_(a)═NH₄) and 60 g of paraffin wax withsoftening point comprised 52° C. and 58° C. The reactor was evacuatedand heated up to 70° C. The reactor was kept under mechanical stirringand loaded with gaseous TFE until reaching a pressure of 20 barg. Thepolymerization was initiated by introducing 30 ml solution containing 4g/l of ammonium peroxodisulfate (NH₄)₂S₂O₈ (APS) and bringingtemperature set point at 80° C. Reaction pressure was maintained at setpoint of 20 barg by feeding gaseous TFE. After having fed 1450 g of TFE,reactor was vented and cooled. A stable PTFE dispersion having a solidcontent of about 32% wt was obtained; no coagulum was formed in thereactor during polymerization. The latex particle diameter was found tobe 230 nm when measured by Laser Light Scattering (LLS).

PTFE dispersion obtained as above detailed was stabilized by addition of4.5% wt. (based on solids) of Tergitol® TMN 100X non-ionic surfactant.The dispersion was diluted to 9% wt. of solids and purified by treatmentwith Amberjet® 4400 OH anion exchange resins. The purified dispersionwas found to contain less than 5 ppm of compound XIII (based on solids).No coagulum was formed during purification process.

Polymerization Example 6 TFE/Perfluoropropylvinyl Ether Copolymerizationin the Presence of Compound VIIa (X_(a)═NH₄) and a PerfluoropolyetherSurfactant

A polymerization reactor having a total volume of 5000 ml equipped witha mechanical stirrer (470 rpm) was charged with 2550 g of deionizedwater, heated at 60° C. and further loaded with 150 g of a 5% wt aqueoussolution of compound XIII (X_(a)═NH₄) and 200 g of a 1% wt aqueoussolution of dicarboxylic perfluoropolyether acid ammonium salt offormula: X_(a)OOC—CF₂O—(CF₂O)_(n)(CF₂CF₂O)_(m)—CF₂—COOX_(a) (X_(a)═NH₄,n, m being such that average molecular weight is 1800. The reactor wasevacuated and heated up to 80° C. The reactor was kept under mechanicalstirring and loaded with gaseous TFE until reaching a pressure of 20barg, and initial charge of 20 g. of perfluoropropylvinylether (PPVE).The polymerization was initiated by introducing 35 ml solutioncontaining 6 g/l of ammonium peroxodisulfate (NH₄)₂S₂O₈(APS) andbringing temperature set point at 80° C. Reaction pressure wasmaintained at set point of 20 barg by feeding gaseous TFE. After havingfed 100 g of TFE, additional perfluoropropylvinylether (PPVE) was fed in5 subsequent amounts corresponding to a total load of 45 g. After havingfed 1300 g of TFE, reactor was vented and cooled. A stable TFE/PPVEcopolymer dispersion having a solid content of about 30% wt wasobtained; no coagulum was formed in the reactor during polymerization.The latex particle diameter was found to be 97 nm when measured by LaserLight Scattering (LLS).

Polymerization Example 7 TFE Polymerization in the Presence of CompoundXIIIa (X_(a)═NH₄) and Subsequent Upconcentration by Clouding

A polymerization reactor with a total volume of 5 l equipped with animpeller agitator was charged with 3 l deionised water. The oxygen freereactor was heated up to 65° C. and the agitation system was set to 500rpm. The reactor was charged with 60 g of paraffin wax, 9 g of compound(XIII, with X_(a)═NH₄), and with TFE to a pressure of 20 barg. Thepolymerization was initiated by 30 cc of a solution composed by 120 mgof ammonium peroxodisulfate (NH₄)₂S₂O₈(APS) and 15 mg of Mohr Salt(NH₄)₂Fe(SO₄)₂6H₂0. As the reaction started, the reaction pressure of 20barg was maintained by the feeding of TFE into the gas fase. Thereaction temperature was increased until 80° C. After 130 min thefeeding of 1600 g of TFE was completed, the monomer valves were closedand the stirring stopped. The reactor was depressurized, vented andcooled. The so obtained polymer dispersion was stable and had a solidcontent of 33% w/w, no coagulum was detected inside the reactor. Thelatex particle diameter was 200 nm according to the Laser LightScattering (LLS) and using DSC analysis the melting point first fusionwas 335° C. and the heat of crystallization was −42 J/g. Said dispersionwas up-concentrated by clouding in a pyrex reactor obtaining a finalcomposition of 74.3% w/w and then formulated to obtain a sample of 600 gcomposed by 60% PTFE, 5.8% Triton® X-100 non ionic emulsifier and havingthe following properties: pH=10.7; viscosity (20° C.)=31.5 cP; viscosity(35° C.)=22.5 cP; conductivity=1132 mS/cm; shear stress stability (61°C.)=627 sec.

A comparative dispersion polymerized in the same way but using APFO assurfactant usually has properties included in the following range:PTFE=59-61%; Triton® X-100 emulsifier=5-7%; pH=9.5-11; viscosity (20°C.)=35 cP max; viscosity (35° C.)=50 cP max; conductivity=800-1300mS/cm; shear stress stability (61° C.)=300-350 sec.

Polymerization Example 8 TFE Polymerization in the Presence of CompoundXIIIa (X_(a)═NH₄) and Recovery of Polymer Thereof as Dry Powder

Step 8a—Polymerization—A polymerization reactor with a total volume of 5l equipped with an impeller agitator was charged with 3 l deionisedwater. The oxygen free reactor was heated up to 70° C. and the agitationsystem was set to 500 rpm. The reactor was charged with 60 g of paraffinwax, 9 g of compound (XIII, with X_(a)═NH₄) of which 5.5 g distributedduring the reaction, and with TFE to a pressure of 20 barg. Thepolymerization was initiated by 16 cc of a solution composed by 8 mg of(NH₄)₂S₂O₈ (APS) and 160 mg of disuccinic acid peroxide (DSAP). As thereaction started, the reaction pressure of 20 barg was maintained by thefeeding of TFE into the gas phase. The reaction temperature wasincreased until 85° C. After 146 min the feeding of 1400 g of TFE wascompleted, the monomer valves were closed and the stirring stopped. Thereactor was depressurized, vented and cooled. The so obtained polymerdispersion was stable and had a solid content of 29% w/w, no coagulumwas detected inside the reactor. The latex particle diameter was 227 nmaccording to the Laser Light Scattering (LLS) and using DSC analysis themelting point first fusion was 338.4° C. and the heat of crystallizationwas −33.3 J/g.

Step 8B—Product Recovery as Dry Powder

The dispersion from step 8a was coagulated, washed and dried for 32hours respectively at 140-160-180° C. According to GC analysis, theresidual amount of compound (XIII) on dried powder was <20 ppm (limit ofthe analysis) in all the three cases.

Recovery Example 9 Adsorption/Desorption of Compound XIII (X_(a)═NH₄) onIon Exchange Resins

4 gr of anionic exchange resin Dowex MSA, previously washed withdemineralized water and drained, were contacted for 24 hours with 100 grof a 1.3% w/w solution of compound (XIII, with X_(a)═NH₄). The resinsaturation was found to be 24.5%.

The so obtained exhausted/saturated resin was washed under vacuum withdemineralized water and drained. A part of this resin, 3.5 gr, after afurther rinsing step (30 ml of water), was extracted with 60 ml of asolution composed by 70% of methanol and 30% of sulphuric acid, andwashed again with 30 ml of water. The acid solution and the rinsingwater were collected, diluted with water, saponificated with NaOH untilpH=11.2 and finally diluted with water until 250 gr. GC analysis showeda recovery of compound (XIII) of 70%.

Polymerization Example 10 Manufacture of a PVDF Latex in the Presence ofMixture of Surfactant

A reactor having an inner volume of 7.57 l was charged with 5241 g ofdeionized water, 134 g of 10% w/w aqueous solution of compound XIII(X_(a)═NH₄), and 5.4 mg of dicarboxylic perfluoropolyether acid ammoniumsalt of formula: X_(a)OOC—CF₂O—(CF₂O)_(n)(CF₂CF₂O)_(m)—CF₂—COOX_(a)(X_(a)═NH₄, n, m being such that average molecular weight is 1800), and4 g of wax. The reactor was heated to 100° C. and vented for 2 min. Thetemperature was increased to 122.5° C. and the reactor was pressurizedwith vinylidene fluoride (VDF) to 650 psi. 24.4 mL of di-tert-butylperoxide were added to the reactor to initiate polymerization, and thepressure was maintained at 650 psi throughout polymerization. Uponreaching target conversion (2298 g of consumed monomer), the monomerfeed and agitation were stopped, the reactor was cooled, and the polymerlatex was collected from the reactor, having a solid content of 28% wtand an average particle size of dispersed polymer particles of 282 nm.The latex was filtered to collect eventual coagulum and the reactor wasinspected to determine the amount of build-up (e.g. polymer stuck ontothe agitation blade and reactor walls).

Polymerization Example 11 TFE/Perfluoropropylvinyl EtherCopolymerization in the Presence of Compound VIIa (X_(a)═NH₄) and aPerfluoropolyether Surfactant Previously Mixed Under the Form of aMicroemulsion

Step 10a—Manufacture of a Stable Dispersion in Water of Compound XIII(with X_(a)═NH₄) and Further Fluorinated Emulsifier

In a glass flask, equipped with a stirrer, were mixed under mildstirring 24.00 g of a surfactant of formula XIII (with X_(a)═NH₄), 24.00g of demineralized H₂O; 12.00 g of a dicarboxylic perfluoropolyetheracid of formula: HOOC—CF₂O—(CF₂O)_(n)(CF₂CF₂O)_(m)—CF₂—COOH (m, m beingsuch that average molecular weight is 1800). The system spontaneouslyformed a microemulsion, which appears as a limpid, thermodynamicallystable dispersion. The droplets average diameter was found to be 11.7 nmwhen measured by Laser Light Scattering (LLS).

Step 10 b—Polymerization of Tetrafluoroethylene (TFE) andPerfluoropropylvinylether (PPVE)

A reactor having inner volume of 5 l was loaded with 3.0 l of water and33 ml of above mentioned microemulsion. Temperature was raised to 75°C.; reactor was loaded with 50 g of perfluoropropylvinylether andpressurized with ethane until increase of 470 mbar, and finallypressurized with TFE at a set-point pressure of 20 bar. Polymerizationwas initiated by addition of ammonium persulfate (0.48 g introduced atthe beginning, 0.30 g further injected in five portions in combinationwith further additions of perfluoropropyl vinylether. Polymerization waspursued until reaching overall monomers consumption of 1500 g after 76min. A latex having a solids content of 31% wt and comprising particleshaving an average diameter (as determined by LLS) of 60 nm of a TFE/PPVEcopolymer (PPVE: 3.1% wt) having a MFI of 30 g/10 min (372° C./5 kg,measured according to ASTM D 1238), a melting point of 305.7° C. and aheat of crystallization of −27.3 J/g (measured according to ASTM D3418).

1. A method for making a fluoropolymer comprising an aqueous emulsionpolymerization of one or more fluorinated monomers wherein said aqueousemulsion polymerization is carried out in the presence of at least onecyclic fluorocompound of the following formula (I):

wherein X₁, X₂, X₃, equal to or different from each other areindependently selected from the group consisting of H, F, and C₁₋₆(per)fluoroalkyl groups, optionally comprising one or more catenary ornon-catenary oxygen atoms; L represents a bond or a divalent group;R_(F) is a divalent fluorinated C₁₋₃ bridging group; Y is a hydrophilicfunction selected from the group consisting of anionic functionalities,cationic functionalities, and non-ionic functionalities.
 2. The methodof claim 1, wherein the hydrophilic function Y of cyclic fluorocompound(I) is selected among non-ionic functions of formulae —(OR_(H))_(n)—OH,wherein R_(H) is a divalent hydrocarbon group, and n is an integer from1 to
 15. 3. The method of claim 1, wherein the hydrophilic function Y ofcyclic fluorocompound (I) is selected from the group consisting ofcationic functions of formulae:

wherein R_(n), equal to or different at each occurrence, represents anhydrogen atom or a C₁₋₆ hydrocarbon group, E is a C₁₋₃ divalenthydrocarbon group and X_(b) ⁻ is an anion selected from the groupconsisting of OH⁻, Cl⁻, Br—, and I⁻.
 4. The method of claim 1, whereinthe hydrophilic function Y of cyclic fluorocompound (I) is selected fromthe group consisting of anionic functions of formulae:

wherein X_(a) is H, a monovalent metal, or an ammonium group of formula—N(R′_(n))₄, wherein R′_(n), equal or different at each occurrence,represents a hydrogen atom or a C₁₋₆ hydrocarbon group.
 5. The method ofclaim 4, wherein the cyclic fluorocompound complies with formula (II)here below:

wherein X₁, X₂, X₃, equal to or different from each other areindependently selected from the group consisting of H, F, and C₁₋₆(per)fluoroalkyl groups, optionally comprising one or more catenary ornon-catenary oxygen atoms; Y is a hydrophilic function selected from thegroup consisting of anionic functionalities, cationic functionalities,and non-ionic functionalities; and R_(F) is a divalent fluorinated C₁₋₃bridging group.
 6. The method of claim 5, wherein the cyclicfluorocompound complies with formula (IV):

wherein X′₁ and X′₂ equal to or different from each other, areindependently a fluorine atom, a —R′_(f) group or —OR′_(f) group,wherein R′_(f) is a C₁₋₃ perfluoroalkyl group, and R_(F) has the samemeanings as in claim 5; and X_(a) is H, a monovalent metal, or anammonium group of formula —N(R′_(n))₄, wherein R′_(n), equal differentat each occurrence, represents a hydrogen atom or a C₁₋₆ hydrocarbongroup.
 7. The method of claim 5, wherein the cyclic fluorocompoundcomplies with formula (VI) here below:

wherein X″₁ and X″₂, equal to or different from each other, areindependently a fluorine atom, a —R′_(f) group or —OR′_(f) group,wherein R′_(f) is a C₁₋₃ perfluoroalkyl group; R_(F) has the samemeaning as in claim 5; and X_(a) is H, a monovalent metal, or anammonium group of formula —N(R′_(n))₄, wherein R′_(n), equal ordifferent at each occurrence, represents a hydrogen atom or a C₁₋₆hydrocarbon group.
 8. The method of claim 4, wherein the cyclicfluorocompound complies with formula (VIII) here below:

wherein R_(F) and X_(a) have the same meanings as in claim 4; X*₁, X*₂equal to or different from each other are independently a fluorine atom,—R′_(f) or —OR′_(f), wherein R′_(f) is a C₁₋₃ perfluoroalkyl group;R^(F) ₁, is F or CF₃, k is an integer from 1 to
 3. 9. The method ofclaim 4, wherein the cyclic fluorocompound complies with formula (XIV)here below:

wherein R_(F) and X_(a) have the same meanings as in claim 4; X*₁, X*₂equal to or different from each other are independently a fluorine atom,—R′_(f) or —OR′_(f), wherein R′_(f) is a C₁₋₃ perfluoroalkyl group;R*_(F) is a divalent fluorinated group, k is an integer from 1 to
 3. 10.The method according to claim 1, being carried out in the presence of amixture of the cyclic fluorocompound of formula (I) and at least onefurther emulsifier different from said cyclic fluorocompound of formula(I), said emulsifier complying with formula: A-R_(f)—B, in which A andB, equal to or different from each other, are —(O)_(p)CFX—COOM*; M*represents H, NH₄, Na, Li or K; X═F or CF₃; p is an integer equal to 0or 1; R_(f) is a linear or branched perfluoroalkyl chain, or a(per)fluoropolyether chain such that the number average molecular weightof A-R_(f)—B is in the range 300 to 3,000.
 11. A cyclic fluorocompoundof formula (IV) or of formula (VI):

wherein X′₁, X′₂, X″₁ and X″₂, equal to or different from each other,are independently a fluorine atom, a —R′_(f) group or —OR′_(f) group,wherein R′_(f) is a C₁₋₃ perfluoroalkyl group, with the provision thatat least one of X′₁ and X′₂ are different from fluorine, and R_(F) is adivalent fluorinated C₁₋₃ bridging group; X_(a) is H, a monovalent metalor an ammonium group of formula —N(R′_(n))₄, wherein R′_(n), equal ordifferent at each occurrence, represents a hydrogen atom or a C₁₋₆hydrocarbon group.
 12. A cyclic fluorocompound complying with formula(VIII) here below:

wherein R_(F) is a divalent fluorinated C₁₋₃ bridging group; X_(a) is H,a monovalent metal or an ammonium group of formula —N(R′_(n))₄, whereinR′_(n), equal or different at each occurrence, represents a hydrogenatom or a C₁₋₆ hydrocarbon group; X*₁, X*₂ equal to or different fromeach other are independently a fluorine atom, —R′_(f) or —OR′_(f),wherein R′_(f) is a C₁₋₃ perfluoroalkyl group; R^(F) ₁, is F or CF₃, kis an integer from 1 to
 3. 13. The cyclic fluorocompound of claim 12,complying with formula (XIII) here below:

wherein X_(a) has the same meaning as in claim
 12. 14. A cyclicfluorocompound complying with formula (XIV) here below:

wherein R_(F) is a divalent fluorinated C₁₋₃ bridging group; X_(a) is H,a monovalent metal or an ammonium group of formula —N(R′_(n))₄, whereinR′_(n), equal or different at each occurrence, represents a hydrogenatom or a C₁₋₆ hydrocarbon group; X*₁, X*₂ equal to or different fromeach other are independently a fluorine atom, —R′_(f) or —OR′_(f),wherein R′_(f) is a C₁₋₃ perfluoroalkyl group; R*_(F) is a divalentfluorinated group, k is an integer from 1 to
 3. 15. The cyclicfluorocompound of claim 14, complying with formula (XVIII) here below:

wherein X_(a) has the same meaning as in claim
 14. 16. A fluoropolymerdispersion comprising at least one cyclic fluorocompound of the formula(I)

wherein X₁, X₂, X₃, equal to or different from each other areindependently selected from the group consisting of H, F, and C₁₋₆(per)fluoroalkyl groups, optionally comprising one or more catenary ornon-catenary oxygen atoms; L represents a bond or a divalent group;R_(F) is a divalent fluorinated C₁₋₃ bridging group; Y is a hydrophilicfunction selected from the group consisting of anionic functionalities,cationic functionalities, and non-ionic functionalities.
 17. A processfor recovering, from the fluoropolymer dispersion of claim 16, a cyclicfluorocompound of formula (I):

wherein X₁, X₂, X₃, equal to or different from each other areindependently selected from the group consisting of H, F, and C₁₋₆(per)fluoroalkyl groups, optionally comprising one or more catenary ornon-catenary oxygen atoms; L represents a bond or a divalent group;R_(F) is a divalent fluorinated C₁₋₃ bridging group; Y is a hydrophilicfunction selected from the group consisting of anionic functionalities,cationic functionalities, and non-ionic functionalities, said processcomprising contacting said fluoropolymer dispersion with a solidadsorbing material.